it is really easy:
1: you need a shape.
2: You just turn the shape.
if you want rotational symmetry:
1: you need a shape that if you rotate it more than once it will look the same, like an equillateral triangle.
2: you rotate it until it looks the same as it did before.
3: rotational symmetry is only true if the item can be rotated more than once and still look the same.